1. Field of the Invention
The present invention relates to a cultivator blade supporting structure, in which a blade of a cultivator can easily be attached to and removed from the structure.
2. Description of the Prior Art
Blades of a cultivator are fitted to the cultivator by inserting a held portion located at one end of each blade into each of a plurality of blade holders projecting from the periphery of a rotation shaft for rotating the blades. As an when required, all the blades attached to the blade holders are removed and replaced with other blades which have different blade shapes.
FIGS. 1 and 2 show a prior art cultivator blade supporting structure. On a periphery 2 of a cultivator blade rotation shaft (hereinafter called the "rotation shaft") 1, there projects a blade holder 3. The cross section of a hollow sleeve 4 of the blade holder 3 perpendicular to an axis X--X of the blade holder 3 has a rhombic shape or a shape of two wedges facing each other. Into the sleeve 4, a stem 6 located at one end of a cultivator blade 5 is inserted. The cross section of the stem 6 has a rhombic shape complimenting the cross section of the sleeve. The stem 6 is fitted to the blade holder 3 with a pin 7 which extends in parallel relationship with the rotation shaft through the blade holder. The stem of the cultivator blade 5 is pivotable around the pin 7.
If the rotation shaft 1 rotates in a direction indicated by an arrow "m" shown in FIG. 3, the cultivator blade 5 is bodily rotated in the same direction. When the inner side of the other end (not shown) of the cultivator blade) 5 hits the ground, the cultivator blade 5 is turned in a direction indicated by an arrow "n" around the pin 7. As a result, the stem 6 in the sleeve 4 is turned with respect to the blade holder 3 in a direction opposite to the rotating direction of rotation shaft 1. The upper end of the stem 6 (FIG. 3) is moved upwardly toward an upper internal edge of the sleeve 4, while a lower end 10 on blade side of the stem is moved toward a lower end portion 11 of the sleeve 4. At both end portions, the wedge shaped edges of the stem 6 are pushed into the wedge shaped portions of the sleeve 4.
A contacting state of the side faces of sleeve 4 and the side faces of stem 6 under the above-mentioned situation is shown in FIGS. 5 and 6 which are enlarged views of the left half of FIG. 3. An upper end 8-1 of an edge 12 of the stem 6 moves to a position 8-2. Namely, in FIG. 6, a corner portion A of the upper end 8-1 moves to a position B, while a corner portion C on the center side moves to a postion C-1. Therefore, a square shape ADFE shown in FIG. 5 is indicated by a rectangular shape BDCA in FIG. 6. A portion outside a face G of the wedge shape portion of sleeve 4, i.e., about the half of the square shape ADFE is in planar contact with the wedge shape portion of the hollow portion.
Initially, the edge 12 of stem 6 contacts the sleeve due to the resilient deformation of the blade holder, but, due to the abrasion of the contacting position, the contacting point is gradually increased to make planar contact as shown in FIG. 6.
The above-mentioned situation is also caused on the right-lower side of pin 7. According to the increase of the area of planar contact, the cultivator blade must be struck in the direction of arrow Z in FIG. 3 to dislodge the stem from the sleeve. However, when this is done, the stem is forced past the neutral position shown in FIG. 1 to a wedged position as shown in FIG. 4. Thus, the cultivator blade must be angularly reciprocated several times before it can be brought to the neutral position of FIG. 1, thereby enabling it to be removed from the holder.